This invention relates in general to computer input devices and in particular to devices for positioning a cursor on a computer screen. For many years the standard computer keyboard has been used for this purpose. However, for many spatial positioning applications, particularly those involving menudriven systems and graphics, the keyboard method is rather slow and difficult to use. Many computers now have a computer input device called a "mouse" that translates arm and hand motion into x-y information to position the cursor on the computer screen. The device, a small, hand-held unit attached to the computer by an umbilical cord or cable, can be moved over a smooth surface such as a desk or work table, moving internal parts which generate signals proportional to the distance the device moves. Operating potentials for the device and output signals from the device are conducted to and from the computer by way of the umbilical cord and processed by an input device to the computer into x and y positions of the cursor on the screen.
Early versions of the mouse utilized potentiometers or variable resistances driven by a ball or wheel projecting through the bottom of the device in contact with a smooth, frictional surface against which the ball or wheel rolls as it is moved over the surface. For the x axis the rotation produces a signal proportional to the amount of rotation for the left and right motion or x direction; in the same manner another potentiometer at a right angle to the first produces a signal for the vertical or y positioning of the cursor on the screen. These first devices worked quite well and were considered an improvement over the keyboard method of cursor positioning. However, the mechanical complexity and the level of resolution of the variable resistance elements of the potentiometers required for accurate positioning were costly and sometimes resulted in low reliability and short life. To increase the reliability of the mouse, optical disc encoders replaced the potentiometers. Optical disc encoders measure the amount of rotation about the x and y axes by optically counting radial stripes on the periphery of the discs and electronically translating the counts into x and y positions of the cursor.
Regardless of the method of generating the electrical signals, positioning the cursor requires coordination between eye and arm to produce a motion similar to that required for locating the position of a paintbrush. This coordinated motion is acquired by practice, but the learning time and ease of use depend upon the level of the operators hand-to-eye motor capability, just as they do when developing a skill for painting. A fairly large desk area usually is needed to obtain full screen motion of the cursor and a correspondingly large range of motion of hand and arm.